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Li H, Wang J, Tjardts T, Barg I, Qiu H, Müller M, Krahmer J, Askari S, Veziroglu S, Aktas C, Kienle L, Benedikt J. Plasma-Engineering of Oxygen Vacancies on NiCo 2O 4 Nanowires with Enhanced Bifunctional Electrocatalytic Performance for Rechargeable Zinc-air Battery. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2310660. [PMID: 38164883 DOI: 10.1002/smll.202310660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Revised: 12/17/2023] [Indexed: 01/03/2024]
Abstract
Designing an efficient, durable, and inexpensive bifunctional electrocatalyst toward oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) remains a significant challenge for the development of rechargeable zinc-air batteries (ZABs). The generation of oxygen vacancies plays a vital role in modifying the surface properties of transition-metal-oxides (TMOs) and thus optimizing their electrocatalytic performances. Herein, a H2/Ar plasma is employed to generate abundant oxygen vacancies at the surfaces of NiCo2O4 nanowires. Compared with the Ar plasma, the H2/Ar plasma generated more oxygen vacancies at the catalyst surface owing to the synergic effect of the Ar-related ions and H-radicals in the plasma. As a result, the NiCo2O4 catalyst treated for 7.5 min in H2/Ar plasma exhibited the best bifunctional electrocatalytic activities and its gap potential between Ej = 10 for OER and E1/2 for ORR is even smaller than that of the noble-metal-based catalyst. In situ electrochemical experiments are also conducted to reveal the proposed mechanisms for the enhanced electrocatalytic performance. The rechargeable ZABs, when equipped with cathodes utilizing the aforementioned catalyst, achieved an outstanding charge-discharge gap, as well as superior cycling stability, outperforming batteries employing noble-metal catalyst counterparts.
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Affiliation(s)
- He Li
- Institute of Experimental and Applied Physics, Kiel University, Leibnizstraße 19, D-24098, Kiel, Germany
| | - Jihao Wang
- Institute of Inorganic Chemistry, Kiel University, Max-Eyth-Straße 2/Otto-Hahn-Platz 6, D-24118., Kiel, Germany
| | - Tim Tjardts
- Chair for Multicomponent Materials, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
| | - Igor Barg
- Chair for Multicomponent Materials, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
| | - Haoyi Qiu
- Chair for Functional Nanomaterials, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
| | - Martin Müller
- Chair for Synthesis and Real Structure, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
| | - Jan Krahmer
- Institute of Inorganic Chemistry, Kiel University, Max-Eyth-Straße 2/Otto-Hahn-Platz 6, D-24118., Kiel, Germany
| | - Sadegh Askari
- Department of Fiber and Polymer Technology, KTH Royal Institute of Technology, Stockholm, SE-10044, Sweden
| | - Salih Veziroglu
- Chair for Multicomponent Materials, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
- Kiel Nano, Surface, and Interface Science KiNSIS, Kiel University, Christian-Albrechts-Platz 4, D-24118, Kiel, Germany
| | - Cenk Aktas
- Chair for Multicomponent Materials, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
| | - Lorenz Kienle
- Chair for Synthesis and Real Structure, Department of Materials Science, Faculty of Engineering, Kiel University, Kaiserstraße 2, D-24143, Kiel, Germany
- Kiel Nano, Surface, and Interface Science KiNSIS, Kiel University, Christian-Albrechts-Platz 4, D-24118, Kiel, Germany
| | - Jan Benedikt
- Institute of Experimental and Applied Physics, Kiel University, Leibnizstraße 19, D-24098, Kiel, Germany
- Kiel Nano, Surface, and Interface Science KiNSIS, Kiel University, Christian-Albrechts-Platz 4, D-24118, Kiel, Germany
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Gore JPP, Mahoney EJD, Smith JA, Ashfold MNR, Mankelevich YA. Imaging and Modeling C 2 Radical Emissions from Microwave Plasma-Activated Methane/Hydrogen Gas Mixtures: Contributions from Chemiluminescent Reactions and Investigations of Higher-Pressure Effects and Plasma Constriction. J Phys Chem A 2021; 125:4184-4199. [PMID: 33966382 DOI: 10.1021/acs.jpca.1c01924] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Wavelength and spatially resolved imaging and 2D plasma chemical modeling methods have been used to study the emission from electronically excited C2 radicals in microwave-activated dilute methane/hydrogen gas mixtures under processing conditions relevant to the chemical vapor deposition (CVD) of diamond. Obvious differences in the spatial distributions of the much-studied C2(d3Πg-a3Πu) Swan band emission and the little-studied, higher-energy C2(C1Πg-A1Πu) emission are rationalized by invoking a chemiluminescent (CL) reactive source, most probably involving collisions between H atoms and C2H radicals, that acts in tandem with the widely recognized electron impact excitation source term. The CL source is relatively much more important for forming C2(d) state radicals and is deduced to account for >40% of C2(d) production in the hot plasma core under base operating conditions, which should encourage caution when estimating electron or gas temperatures from C2 Swan band emission measurements. Studies at higher pressures (p ≈ 400 Torr) offer new insights into the plasma constriction that hampers efforts to achieve higher diamond CVD rates by using higher processing pressures. Plasma constriction is proposed as being inevitable in regions where the local electron density (ne) exceeds some critical value (nec) and electron-electron collisions enhance the rates of H2 dissociation, H-atom excitation, and related associative ionization processes relative to those prevailing in the neighboring nonconstricted plasma region. The 2D modeling identifies a further challenge to high-p operation. The radial uniformities of the CH3 radical and H-atom concentrations above the growing diamond surface both decline with increasing p, which are likely to manifest as less spatially uniform diamond growth (in terms of both rate and quality).
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Affiliation(s)
- Joseph P P Gore
- School of Chemistry, University of Bristol, Bristol, U.K. BS8 1TS
| | - Edward J D Mahoney
- School of Chemistry, University of Bristol, Bristol, U.K. BS8 1TS.,Centre for Doctoral Training in Diamond Science and Technology, University of Warwick, Gibbet Hill Road, Coventry, U.K. CV4 7AL
| | - James A Smith
- School of Chemistry, University of Bristol, Bristol, U.K. BS8 1TS
| | | | - Yuri A Mankelevich
- Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991, Russia
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Li H, Zhou Y, Donnelly VM. Optical and Mass Spectrometric Measurements of the CH 4-CO 2 Dry Reforming Process in a Low Pressure, Very High Density, and Purely Inductive Plasma. J Phys Chem A 2020; 124:7271-7282. [PMID: 32791834 DOI: 10.1021/acs.jpca.0c04033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper presents a study of a CH4-CO2 plasma-reforming process carried out in a high power density (5-50 W/cm3), using toroidal transformer-coupled plasma, and operated at low pressure (0.2-0.7 Torr). Using the intermediate between a thermal and nonthermal plasma (electron density, ne ≈ 3 × 1012 cm-3 and a maximum gas temperature of ∼4000-6000 K along the center line), the low-pressure study provides a unique set of conditions to investigate reaction mechanisms, where three-body reactions can be ignored. Reactive species in the plasma were identified by optical emission spectroscopy. End products of the reforming process were measured by mass spectrometry. Quite high conversions of CO2 and CH4 were found (90%), with selectivities for CO and H2 of 80% at 300 sccm feed gas flow rate in a 0.5 Torr plasma, with a mole ratio CO2-CH4 of 1:1. A detailed reaction mechanism is presented, taking into account the combined detection of reactive intermediates in the plasma (H, O, CH, and C2) and stable product downstream.
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Affiliation(s)
- Hanyang Li
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204, United States
| | - Yingliang Zhou
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204, United States
| | - Vincent M Donnelly
- Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204, United States
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Mahoney EJD, Lalji AKSK, Allden JWR, Truscott BS, Ashfold MNR, Mankelevich YA. Optical Emission Imaging and Modeling Investigations of Microwave-Activated SiH 4/H 2 and SiH 4/CH 4/H 2 Plasmas. J Phys Chem A 2020; 124:5109-5128. [DOI: 10.1021/acs.jpca.0c03396] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Edward J. D. Mahoney
- School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
- Centre for Doctoral Training in Diamond Science and Technology, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, U.K
| | | | | | | | | | - Yuri A. Mankelevich
- Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Leninskie gory, Moscow 119991, Russia
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Mahoney EJD, Rodriguez BJ, Mushtaq S, Truscott BS, Ashfold MNR, Mankelevich YA. Imaging and Modeling the Optical Emission from CH Radicals in Microwave Activated C/H Plasmas. J Phys Chem A 2019; 123:9966-9977. [PMID: 31647649 DOI: 10.1021/acs.jpca.9b08345] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a combined experimental/modeling study of optical emission from the A2Δ, B2Σ-, and C2Σ+ states of the CH radical in microwave (MW) activated CH4/H2 gas mixtures operating under a range of conditions relevant to the chemical vapor deposition of diamond. The experiment involves spatially and wavelength resolved imaging of the CH(C → X), CH(B → X), and CH(A → X) emissions at different total pressures, MW powers, C/H ratios in the source gas, and substrate diameters. The results are interpreted by extending an existing 2D (r, z) plasma model to include not just electron impact excitation but also chemiluminescent (CL) bimolecular reactions as sources of the observed CH emissions. Three possible CL reactions (of H atoms with CH2(a1A1) and CH2(X3B1) radicals and of C(1D) atoms with H2) are identified as plausible sources of electronically excited CH radicals (particularly of the lowest energy CH(A) state radicals). Each or all of these could contribute to the observed emissions and, collectively, are deduced to be the major source of the CH(A) emissions observed at the high temperatures (Tgas ∼ 3000 K) and pressures (75 ≤ p ≤ 275 Torr) explored in the present study. We suggest that such CL contributions are likely to be commonplace in such high pressure, high temperature plasma environments and highlight some of the risks associated with using relative emission intensities as an indicator of the electron characteristics in such plasmas.
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Affiliation(s)
- Edward J D Mahoney
- School of Chemistry , University of Bristol , Bristol , U.K. BS8 1TS.,Centre for Doctoral Training in Diamond Science and Technology , University of Warwick , Gibbet Hill Road , Coventry , U.K. , CV4 7AL
| | - Bruno J Rodriguez
- School of Chemistry , University of Bristol , Bristol , U.K. BS8 1TS.,Centre for Doctoral Training in Diamond Science and Technology , University of Warwick , Gibbet Hill Road , Coventry , U.K. , CV4 7AL
| | - Sohail Mushtaq
- School of Chemistry , University of Bristol , Bristol , U.K. BS8 1TS
| | | | | | - Yuri A Mankelevich
- Skobeltsyn Institute of Nuclear Physics , Lomonosov Moscow State University , Leninskie gory, Moscow , 119991 , Russia
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